8mm Forum: 24 FPS Chatter on Sound Track?

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Posted by Steve Klare (Member # 12) on July 01, 2007, 07:29 PM:

So, for a couple of years I've been operating my Elmo ST-800 on the dining room table and projecting on a screen in the living room. I decided to make the big leap: open up the porch doors, move the projector back about 8 feet and put some speakers up by the screen. I figure moving the machine further away from the audience and moving the source of the sound closer means the projector noise will be less intrusive.

It works...almost.

There is a chatter in the sound track that sounds almost exactly like the mechanical sound of the shutter/claw etc. I bet it has always been there, but when the machine is in the same room the mechanical sound drowns out the lower level sound through the speakers.

The interesting part of it is when the sound track is quiet, the chatter goes away, but when the level goes up, the chatter goes with it, as if it is modulating the audio.

Any ideas??

Thanks!

Posted by Osi Osgood (Member # 424) on July 01, 2007, 08:56 PM:

Sounds like a problem with the film loop. Lets see, I'm bad at wording these technical things ...

The film is either "snapping" or "vibrating" as it goes into the sound heads. I doubt it has much to do with the claw.

But then, what the heck do I know?

Posted by Gary Crawford (Member # 67) on July 02, 2007, 08:06 AM:

Some of our more technical minded members can help more with this, but the super 8 clattering effect has plauged the format since it began. Old Standard 8mm had a long 56 frame separation between the intermittent movement of the film required at the gate...and the smooth running movement required at the playback head...plenty of time for a big capstan and roller combo , along with a flywheel to smooth out the flow. BUT on super 8 , the gate and sound head are only a second apart...(18 frames?)...anyway....a very short distance. rollers and capstans are smaller...and they have to be working almost perfectly....to smooth out that intermittent movement of the film. Also ...the sharp curve of the film coming out of the gate doesn't help. The problem is better or worse, depending on many things, including lubrication of the film. A clean well lubed film seems to do better. Clean good rubber on the capstan roller is a big help, too. The problem used to be worse in the early days of super 8 when soundtracks were recorded on projectors...all linked up together and recording at real time. The intermittent clatter was first sometimes recorded on the film to begin with....then when we got the film on our home projectors , the clattering of our machines was added to what was already recorded on the track.
Finally some say the problem seems less on color films of recent vintage...thinner stock.....some say older acetate films are less clattery.
Finally, if the projector is not setting that bottom loop exactly right, the film hits on the guides...and that just makes it jump even more...and the roller and capstan can't quite smooth it out. I'm sure there are technical folks who can add or subtract or correct me on these things, but this has been my experience and this is what some other experts have told me.

Posted by Maurizio Di Cintio (Member # 144) on July 02, 2007, 09:11 AM:

I agree with all that has been posted so far, at least in general terms.

What I fail to realize is this: usually Elmo machines are void of this problem, because they either have an additionl pinch roller before the head assembly (like in the GS 1200), or the very sound pressure pads are replaced by a rubber roller (as I've seen on the ST 1200).
Does this sspecific model differ significantly from the ones I mentioned?
(sorry I can't be of help, but for one thing: could it also depend on a not perfect claw movement? That is perhaps it engages the sprockets a little bit too outer or inner as opposed to the ideal side pitch of the sprockets...)

Posted by Gary Crawford (Member # 67) on July 02, 2007, 10:12 AM:

I run Elmo's St 1200 Hd's...and also an AT800...and have had this clatter , more or less...on all of the machines on some films....even when the machines were new. If those rollers are engaging that film's surface and really smoothing the motion, films will clatter. ON some films....no clatter at all. Others can be quite noisey.
I suspect how the machine threads also my affect it. I have run a film on a machine...and get clatter. Then run it again on the same machine the same night and it's smooth. With the short picture to sound separation of Super 8, even a frame or two difference in the size of the bottom loop seems to have an effect on clatter.

Posted by Kevin Faulkner (Member # 6) on July 02, 2007, 10:33 AM:

Maurizio is spot on. You will find it more noticeable on soundtracks which are quite loud.
It's a common problem on all the Elmos to varying degrees and other makes of machines but should not be heard too much on the GS1200 because of the pinch roller at the entrance of the sound head.

Yes the distance between the picture gate and the sound head on super 8 is too short really to smooth out the intermittent movement in that short time but the roller on the GS is a real improvement and virtually removes that problem.

Sorry Steve there is not much you can do to cure that particular problem which as you have found is more noticeable once you remove the audible, mechanical sound from the projector which obviously masks the noise (flutter).

Kev.

Posted by Steve Klare (Member # 12) on July 02, 2007, 09:15 PM:

Thanks for your help gents!,

Lubrication is definitely a factor. I tried Tim Christian's trick of lubing up the guides with furniture polish and it reduced the problem from obnoxious to better than tolerable, even for the worst film.

The order of the film path for the ST-800 is gate, loop, heads and then the pinch roller.

Posted by Kevin Faulkner (Member # 6) on July 03, 2007, 04:00 AM:

The forward loop on the ST1200 and early GS1200 can be quite bad for this flutter noise.
On the ST600 and related machines they changed the film path which is supposed to have reduced this effect and of course they also employed that new layout on later GS1200's.
On my own GS1200 Xenon with the roller in front of the heads the noise is non existent but remove that small roller and it comes back with a vengeance but only on highly modulated soundtracks.
Never heard the problem on Optical sound but then the gap between picture and sound is longer so the flutter is smoothed out more.

In my experiences I have found the Poly stocks to be less clattery and I do agree that lubrication on older stocks helps to reduce the noise but its not possible to eliminate it completely except by design or modification to the machine. Yes the size of the loop will also effect the noise.

Kev.

Posted by Paul Adsett (Member # 25) on July 03, 2007, 11:54 AM:

I have to say Kev that I have never heard any flutter on the Eumig 900 series machines. The pinch roller and capstan on the Eumig's is very much larger than on the Elmo's, so this may be the reason why. Another factor may be that on the Eumig's the film path goes through a 90 degree angle loop before entering the (horizontal plane) sound head, thus effectively isolating the intermittent motion of the film coming out of the (vertical plane) gate. The corresponding angle on the Elmo's seems to be more like 45 degrees, which may not be enough to get total isolation of the film jerkiness. Also, on the GS1200's I have noticed that it is possible for the uneveness of the take up spool to sometimes transfer through the lower sprocket and cause up and down fluctuations in the black plastic tension arm, which presumably could influence the smoothness of the film velocity across the sound head. None of these problems are present on the Eumig 900's which have a much simpler film path, and possibly have the best sound reproduction of any super 8 machine. I'm not knocking Elmo's here, they are truly superb machines, but I think it's worth pointing out that in some areas 'The Wizards of Vienna' did a better job than the Japanese.

Posted by Dan Lail (Member # 18) on July 03, 2007, 01:18 PM:

Steve, I had that problem on my ST-800 too. Keeping the pinch roller clean with rubber cleaner(not alcohol) and keeping proper pinch roller pressure is paramount. Lubricating the film with Film Guard will reduce or eliminate the problem and improve the picture quality.

Another way to quite the projector itself is to put a shock absorbent pad between it and the surface it is sitting on.

Posted by Kevin Faulkner (Member # 6) on July 03, 2007, 05:46 PM:

Paul, the sound is very often masked by the intermittent sound from the projector.
If you put a pair of headphones on and listen to a well modulated sound track you may find even the Eumig suffers from this clicking noise.
Its like Tinnitus...you can eliminate the noise by adding noise. Remove the external noise and the problem becomes apparent which is what has happened in Steve's case. [Frown]

Kev.

Posted by Steve Klare (Member # 12) on July 03, 2007, 08:21 PM:

Yes,

I can see this leading to the projectors staying in the dining room, even with the speakers up next to the screen. I guess to some extent, I actually need their sound!

It's not all bad, though. I found the hike through the living room and dining room out onto the porch every time there was a projector tweak or a reel change was a little awkward.

Dan, exactly what is rubber cleaner? (No comments from the peanut gallery!)

Posted by Dan Lail (Member # 18) on July 03, 2007, 10:55 PM:

Steve, it's called Caikleen;

Never leave home without it! [Big Grin]

Posted by Maurizio Di Cintio (Member # 144) on July 07, 2007, 03:33 AM:

This problem affects S/8 to various degrees and I guess it must depend on a combination of design and claw registration, i.e. how much stress the tooth (teeth) puts onto the sprocket causing an almost imperceptible jerk. For example if the sprokects are engaged a little too on the outer/inner side, then, given the "circular" nature of claw's movement (don't forget its arm is hinged), the film may vibrate in the gate more than desirable, thus causing the kind of problem we're talking about.

Sankyo's seem particularly prone to this if the claw is even a spllit-hair out of position. Eumigs are a little more forgiving.
My ELmo GS 1200 is a beauty even if I listen its playback via headphones: no clatter at all on any frequency whatsoever, in fact I think its claw must have been very well fine-tuned.

Of course using lubricants may improve the situation even in not perfectly tuned machines, but they cant eliminate the problem.

Posted by Eric Baucher (Member # 809) on July 08, 2007, 12:15 PM:

I have an Elmo ST1200HD and it only does that on occasion. I'm even running a technics speaker (3way) as an external speaker. I really wish I could run two speakers off the back two plugs without going through an amp, but I dont have the right chord for the 1200 end.

Posted by Steve Klare (Member # 12) on October 27, 2007, 08:53 PM:

I have an interesting development on this one. I was cleaning the machine tonight when I noticed the rubber roller is semi-loose on the brass hub that mounts it to the flywheel shaft. I'm pretty sure that this means the inertia of the flywheel isn't as effective as far as smoothing out the film speed past the sound heads, since the roller can slip a little bit when it's torqued.

The roller looks like it's in good shape. Is it supposed to be secured to the hub by some kind of adhesive?

Posted by Kevin Faulkner (Member # 6) on October 28, 2007, 05:54 PM:

Steve, What is actually turning. Certainly if you were to hold the flywheel you can still turn the capstan.

The flywheel/Capstan is designed to have some slip. This is what the spring clip in the centre of the flywheel is for.

Kev.

Posted by Steve Klare (Member # 12) on October 28, 2007, 08:53 PM:

Hi Kevin

I had thought that the roller was rotating freely on it's hub, but on closer examination the flywheel slips on it's shaft as you say.

I guess this allows the flywheel to gradually catch up to film speed without dragging the roller on the film surface? Kind of a clutch?

I guess we'll file that under something learned every day...

Thanks!

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